the pivot bolt that connects the body of a horse-drawn carriage to the front axle and provides the steering joint
b.
a similar bolt placed between a railway carriage and the bogies
kingbolt in American English
(ˈkɪŋˌboʊlt)
noun
any main bolt; esp., one that acts as a vertical pivot for a turning vehicle, as that connecting the front axle of a wagon, etc., or the truck of a railroad car, with the body